The present invention relates generally to ink-jet printers and, more particularly, to a printhead assembly for use in such printers, and the method of using the same.
Modern printing devices utilize a printhead or drop ejector mounted in a carriage that is moved back and forth across print media, such as paper for example. As the printhead moves across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text.
While such conventional printing devices have substantial value and are useful in many applications, in some cases conventional printers have serious limitations. For example, a requirement exists for increasing the throughput, or output rate, of inkjet printers for commercial applications. These applications include document copying, print on demand, and document customization. As a general rule, such applications require rapid generation of printed documents, without sacrificing print quality.
While recognizing the limitations of conventional in satisfying high speed printing requirements, printer designers have considered several approaches. One approach is to develop a new printhead with an increased firing frequency. Such a printhead would, no doubt, have great value. However, the costs of research, development and manufacture of such a printhead, and inks compatible therewith, render this solution unacceptable for current requirements.
Since getting the ink onto the media rapidly is a design objective, another conventional solution to the high speed/high print quality goal is to increase the number of printheads supported by the printhead carriage. In general, the printhead surface facing the media is substantially rectangular and elongated, having an orifice plate located adjacent an end of the facing surface. One conventional solution to the problem has been to deploy 8 to 12 printheads, arrayed in two parallel rows, wherein the print media travels perpendicularly to the row axes.
While this approach can increase printer throughput, it often does so at the expense of print quality. This is the case because, no matter how close together the parallel printhead rows are, there will still be a distance between opposing printhead orifice plates. As a result, as the media travels past the parallel rows, there will be a time when no printing is occurring. This presents two problems when paper is the print media.
It is recognized that paper tends to cockle, or swell up, as it is whetted during the printing process. The cockle problem presents the printer designer with a formidable problem. Simply put, while trying to increase throughput by placing multiple printheads in parallel rows, the time when printing is not occurring increases the likelihood of cockling of the paper. In addition, the dwell time, or print delay in the parallel row design, sometimes results in ink and media interactions. This is an undesirable outcome since it can produce hue shift, resulting in banding on the printed media.
In view of the problems inherent in the parallel printhead row design, another approach has been tried. In this case, multiple printheads have been arrayed in a pair of staggered rows with the objective of keeping ink on the media at all times during the printing process. This concept has value since it lessens substantially the hue shift problem. A shortcoming, however, is that this design requires a long media print zone and it is necessary to hold the media flat for an extended period of time. The long print zone, of course, tends to exacerbate the cockling problem.
From the foregoing it will be apparent that conventional solutions to the high throughput and high print quality challenge are not satisfactory. Thus, there is a need for a printing technique whereby this challenge is met without expenditure of money and effort to design a new printhead. Desirably, such a technique would afford increased throughput while enabling a high level of print quality while avoiding the limitations of hue shift and media cockle.
According to the present invention, there is provided an ink-jet printhead assembly comprising an elongated printhead carriage for supporting a plurality of printheads for movement across a path of travel of print media. The carriage includes a pair of ends and a region disposed equidistant the ends. The carriage supports a pair of staggered printhead arrays and each one of the pair of printhead arrays includes a plurality of spaced apart printheads. At least two of the plurality of printheads have an orifice plate having an edge disposed adjacent the central region, wherein the centrally disposed edge of each one of the orifice plates is collinear with an edge of each of the other centrally disposed orifice plates.
The present invention affords several advantages. It effectively doubles throughput, in pages per minute, over the conventional 4 printhead carriage array. Thus, without the costs and effort for new development in increasing firing frequency of a new printhead, existing printheads can be used in the invention to deliver increased throughput. Further, expensive ink and printhead development costs are avoided since existing printheads can be utilized.
Another advantage of the present invention is its inherent compatibility with existing writing system processes such as data pipeline, printhead servicing and print modes.
Further, printhead reliability and life issues are well known, in contrast to the situation wherein a new printhead would be employed. Printhead carriage design is simplified since such design can be leverage because of familiarity with the printhead. Finally, the time to market of the present invention is substantially shortened because of the elimination of a new printhead development program.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.